This is a 371 of PCT/KR98/00119 filed May 12, 1998.
1. Field of the Invention
The present invention relates to an aqueous cellulose solution and a rayon fiber produced from the same, and more particularly, to an aqueous cellulose solution containing chitosan and/or chitosan derivatives, or alginic acid and/or alginic acid derivatives, and a water-soluble and antibacterial rayon fiber produced from the solution.
2. Description of the Related Art
In general, a polymer such as rubber, leather, paper, plastic and fiber is not soluble in water. However, water-soluble polymers are also important even though such kind of polymer are few. Water-soluble polymers have been widely used in pharmaceuticals, cosmetics, foods and fiber industries.
Meanwhile, cellulose as a major component of a cell membrane of plants is a linear polymer substance in which D-glucose units are connected by a xcex2-glucosidic ether bond. Cellulose is not soluble in water due to strong internal bond such as intra- and inter-molecular hydrogen bonds, inter-molecular van der Waals bonds, and high degree of crystallinity caused from intrinsic rigidity. Thus, in order to make cellulose water-soluble, intra- and inter-molecular hydrogen bonds, and inter-molecular van der Waals bonds must be broken. Such solubilized cellulose includes carboxymethyl cellulose, hydroxypropyl cellulose, sulfated cellulose, etc. However, these cellulose are cellulose derivatives which cannot be regenerated back into cellulose because their molecular structures are permanently changed.
In order to produce rayon fiber while maintaining the molecular structure of cellulose, cellulose solution containing sodium cellulose xanthate or cuprammonium cellulose is prepared, and then spun into a coagulating bath, thereby regenerating cellulose. However, reagent such as carbon disulfide CS2 and Schweitzer""s reagent, used to prepare the cellulose solution containing cellulose xanthate or cuprammonium cellulose, are fatally poisonous to humans and pollutes the environment.
Thus, researches have been actively and widely conducted to find a method to solubilize cellulose while minimizing the current pollution problems. As a result, DMF/N2O4 solvent, DMSO/paraformaldehyde solvent, NH3/NH4SCN solvent, DMAc/LiCl solvent, and NMMO (N-methylmorpholine-N-oxide) solvent have been developed. However, cellulose solutions prepared by such solvent systems are organic solutions, not aqueous solutions, so that costs required for recovering the solvents are high.
Thus, the present inventor has conducted numerous experiments to obtain an aqueous cellulose solution without causing the above problems, and provided an aqueous cellulose solution in a homogeneous phase. The aqueous cellulose solution is obtained by mixing ambidextrous cellulose having a negative charge or positive charge depending on the peripheral circumstances with a water-soluble polymer having the same negative or positive charge as that of the ambidextrous cellulose. Accordingly, in the aqueous solution, cellulose is easily dispersed into the water-soluble polymer by the electrical repelling force, thus providing homogeneous aqueous cellulose solution in which cellulose is mixed with the water-soluble polymer homogeneously at the molecular level. Also, the present inventor has noticed that a fiber or film formed by wet-spinning the homogeneous cellulose solution into a coagulating bath such as low-temperature water or acetone has water-soluble or water-resistant property depending on the composition of the coagulating bath, and also has antibacterial property.
To solve the above problems, it is an objective of the present invention to provide an aqueous cellulose solution capable of minimizing the problems of pollution.
It is another objective of the present invention to provide a rayon fiber produced from the aqueous cellulose solution.
Accordingly, to achieve the first objective, there is provided an aqueous cellulose solution comprising: a first component containing at least one selected from the group consisting of alkali cellulose and cellulose derivatives; and a second component containing at least one selected from the group consisting of soluble chitosan and chitosan derivatives, or alternatively at least one selected from the group consisting of soluble alginic acid and alginic acid derivatives, wherein the first and second components are homogeneously mixed without phase separation.
To achieve the second objective, there is provided a rayon fiber produced by wet-spinning an aqueous cellulose solution into a coagulating bath, wherein the aqueous cellulose solution comprises: a first component containing at least one selected from the group consisting of alkali cellulose and cellulose derivatives; and a second component containing at least one selected from the group consisting of soluble chitosan and chitosan derivatives, or alternatively at least one selected from the group consisting of soluble alginic acid and alginic acid derivatives, and the first and second components are homogeneously mixed without phase separation.
Preferably, the total content of the first and second components is 4xcx9c12 wt % based on the total weight of the cellulose solution.
Preferably, the cellulose derivative is at least one selected from the group consisting of carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, sulfated cellulose, methyl cellulose, ethyl cellulose, n-propyl cellulose and isopropyl cellulose.
Preferably, the chitosan derivative is at least one selected from the group consisting of alkali chitin, carboxymethyl chitin, hydroxypropyl chitosan, sulfated chitosan, succinyl chitosan, chitosan lactate, sodium chitosan acetate and quaternary ammonium salt of chitosan.
Preferably, the quaternary ammonium salt of chitosan is at least one selected from the group consisting of trimethylammonium chitosan halide, triethylammonium chitosan halide and triisopropylammonoum chitosan halide.
Preferably, the alginic acid derivative is at least one selected from the group consisting of sodium alginate, calcium alginate, potassium alginate and magnesium alginate.
Preferably, the cellulose solution further comprises a base compound of 0.01xcx9c5 wt % based on the total weight of the cellulose solution, and the base compound is at least one selected from the group consisting of sodium hydroxide (NaOH), potassium hydroxide (KOH), calcium hydroxide (Ca(OH)2) and magnesium hydroxide (Mg(OH)2).
Preferably, the coagulating bath is water.
Preferably, the coagulating bath is water containing 5xcx9c25 wt % of at least one selected from the group consisting of zinc sulfate, sodium sulfate, ammonium sulfate, sodium chloride and calcium chloride.
Preferably, the coagulating bath is water containing 3xcx9c8 wt % of at least one selected from the group consisting of chitosan and chitosan derivatives, and 5xcx9c25 wt % of at least one selected from the group consisting of zinc sulfate, sodium sulfate, ammonium sulfate, sodium chloride and calcium chloride.
Preferably, the coagulating bath is water containing 3xcx9c8 wt % of at least one selected from the group consisting of alginic acid and alginic acid derivatives, and 5xcx9c25 wt % of at least one selected from the group consisting of zinc sulfate, sodium sulfate, ammonium sulfate, sodium chloride and calcium chloride.
Preferably, the temperature of the coagulating bath is 4xcx9c15xc2x0 C.
An aqueous cellulose solution of the present invention is obtained by dissolving a mixture containing alkali cellulose and/or cellulose derivatives as a first component, and a water-soluble chitosan and/or derivatives thereof, or a water-soluble alginic acid and/or derivatives thereof, as a second component, in water at room temperature.
In the present invention, in general, cellulose can be separated and purified from wood. Cellulose and cellulose derivatives having a degree of polymerization of 300xcx9c600 are favorable in terms of convenience in the spinning process, and material properties of rayon fiber produced therefrom. If the degree of polymerization is less than 300, mechanical strength of the rayon fiber obtained therefrom is not satisfactory. If the degree of polymerization exceeds 600, it is difficult to smoothly perform the solubilization. Cellulose may be obtained from cotton linter or recycled rayon and paper other than wood pulp.
In the present invention, because cellulose is water-insoluble alkali cellulose is used, which is allowed to swell through a pre-treatment using a base compound. Also, cellulose derivatives used in the present invention other than alkali cellulose include carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, sulfated cellulose, methyl cellulose, ethyl cellulose, n-propyl cellulose and isopropyl cellulose. Because the cellulose derivatives dissolve well in water, the pre-treatment using the base compound is not necessary.
Chitosan is a polysaccharide obtained by deacetylating chitin. That is, after treating the shell of Crustacea, the insect species and mold with acid, a treatment using a base compound is performed to separate and purify protein and calcium carbonate, resulting in chitin. Then, the obtained chitin is heated in sodium hydroxide solution for deacetylation. Chitosan, showing excellent water-retention properties, has similar molecular structure to cellulose, so it can be mixed homogeneously with cellulose. Also, amino group coupled to C2 of a glucose ring of the chitosan is basic, that is, positive ionic, so chitosan and derivatives thereof bind with microbes, dye, acid rain, etc. having negative ionic property, thereby providing antibacterial properties and improved dyeing property and acid rain neutralizing property.
In the present invention, xe2x80x9csoluble chitosanxe2x80x9d means a water-soluble chitosan whose degree of deacetylation is controlled to approximately 45xcx9c55% during the deacetylation from chitin. If chitosan changes into chitosan derivatives, solubility increases. In particular, if the amino group becomes a quaternary ammonium salt, positive ionic property increases, thereby further improving solubility, antibacterial and dyeing properties, and acid rain neutralizing property.
Chitosan derivatives used in the present invention includes alkali chitin, carboxymethyl chitin, hydroxypropyl chitosan, sulfated chitosan, succinyl chitosan, chitosan acetate, chitosan lactate, sodium chitosan acetate and quaternary ammonium salt of chitosan. The quaternary ammonium salt chitosan includes trimethylammonium chitosan halide, triethylammonium chitosan halide and triisopropylammonoum chitosan halide. The quaternary ammonium salt chitosan is obtained by reacting the amino group of chitosan with alkyl halide. Alkyl halide for this purpose includes methylchloride, methyliodide, methylbromide, ethylchloride, methyliodide, ethylbromide, n-propylchloride, n-propyliodide, n-propylbromide, isopropylchloride, isopropyliodide and isopropylbromide. If an alkyl halide having a longer alkyl group than methyl, ethyl, propyl and isopropyl is used, the reaction into the quaternary ammonium salt is slow and difficult to occur.
Alginic acid is a polysaccharide obtained by processing a sodium carbonate extraction solution of dry seaweed such as brown seaweed and tangle with acid. Alginic acid has the same molecular structure as cellulose except that hydroxymethyl group coupled to C6 of glucose ring is substituted by a carboxyl group, so it can be mixed homogeneously with cellulose. Alginic acid has excellent water-retention properties, a slight antibacterial property, and flame retardancy. Alginic acid can be solublized in water by processing with a base compound such as sodium hydroxide (NaOH). In particular, alginic acid derivatives such as sodium alginate, calcium alginate, potassium alginate and magnesium alginate are highly soluble in water.
The aqueous cellulose solution of the present invention is a homogeneous mixture, without phase separation, of a first component containing the alkali cellulose or cellulose derivatives, and a second component containing soluble chitosan or chitosan derivatives. Here, the content of the second component is 0.1xcx9c50 wt % based on the total weight of the first component, and the second component may be alginic acid or an alginic acid derivative instead of chitosan or an chitosan derivative. If the content of the second component is less than 0.1 wt %, the antibacterial property of the rayon fiber produced from the cellulose solution is poor. On the other hand, if the content of the second component exceeds 50 wt %, mechanical properties of the resultant rayon fiber are lowered.
Also, the aqueous cellulose solution of the present invention may further include a base compound which has not been completely removed after alkali cellulose, chitosan and/or chitosan derivatives, or alginic acid and/or alginic acid derivatives are obtained. The base compound includes sodium hydroxide (NaOH), potassium hydroxide (KOH), calcium hydroxide (Ca(OH)2) and magnesium hydroxide (Mg(OH)2). The base compound is controlled to be 0.01xcx9c5 wt % based on the total content of the aqueous cellulose solution. If the content of the base compound exceeds 5 wt %, cellulose does not solubilize well.
The aqueous cellulose solution of the present invention is mainly used for making rayon fiber. However, the aqueous cellulose solution can be applied to food and cosmetics industries. That is, in the aqueous cellulose solution, the cellulose is easily decomposed by yeast or bacteria into oligomers such as cellopentaose and cellohexaose, or monomers such as glucose. Here, the obtained oligomers are used as raw material for cosmetics industry, and the monomers by the food industry. Also, the rayon fiber obtained by spinning the aqueous cellulose solution has an antibacterial property or flame retardancy as well as the intrinsic properties of the cellulose fiber such as a high hygroscopic property and a suitable mechanical property. Here, the antibacterial property or flame retardancy is caused by addition of chitosan and/or chitosan derivatives or alginic acid and/or alginic acid derivatives.
Hereinafter, a method of producing rayon fiber using the cellulose solution will be described.
The rayon fiber is obtained by wet-spinning the aqueous cellulose solution into a coagulating bath at a low temperature. Preferably, the temperature of the cellulose solution is controlled to be 15xcx9c25xc2x0 C. If the temperature of the solution is less than 15xc2x0 C., spinning is difficult due to high viscosity. Meanwhile, if the temperature of the solution is higher than 25xc2x0 C., the texture of the fiber is not smooth because the rayon fiber is rapidly cooled in the coagulating bath. Preferably, the coagulating bath is water of 4xcx9c15xc2x0 C. (first coagulating bath) containing 5xcx9c25 wt % of at least one selected from the group consisting of zinc sulfate, sodium sulfate, ammonium sulfate, sodium chloride and calcium chloride, water of 4xcx9c15xc2x0 C. (second coagulating bath) containing 3xcx9c8 wt % of chitosan and/or chitosan derivatives and 5xcx9c25 wt % of at least one selected from the group consisting of zinc sulfate, sodium sulfate, ammonium sulfate, sodium chloride and calcium chloride, or water of 4xcx9c15xc2x0 C. (third coagulating bath) containing 3xcx9c8 wt % of alginic acid or alginic acid derivatives and 5xcx9c25 wt % of at least one selected from the group consisting of zinc sulfate, sodium sulfate, ammonium sulfate, sodium chloride and calcium chloride. Also, the coagulating bath may be water of 4xcx9c15xc2x0 C. or acetone of 10xcx9c15xc2x0 C. containing no additives such as inorganic salts, chitosan, chitosan derivatives, alginic acid, or alginic acid derivatives.
When spinning the aqueous cellulose solution into the coagulating bath, electric charges of cellulose are neutralized by the additives of the coagulating bath, and hydration water is decreased, causing coagulation. The obtained rayon fiber shows water-solubility at approximately 40xcx9c90xc2x0 C. Meanwhile, in order to produce a rayon fiber which is resistant to boiling water, the third coagulating water must be used when the soluble chitosan and/or chitosan derivatives are used as the second component of the aqueous cellulose solution, and the second coagulating water when the alginic acid and/or alginic acid derivatives are used as the second component. This is because chitosan and/or chitosan derivatives, which is a positive ion polyelectrolyte of the aqueous cellulose solution, are electrically coupled with alginic acid and/or alginic acid derivatives, which is a negative ion polyelectrolyte of the coagulating bath, or alginic acid and/or alginic acid derivatives, which is a negative ion polyelectrolyte of the aqueous cellulose solution, are coupled with chitosan and/or chitosan derivatives, which is a positive ion polyelectrolyte of the coagulating bath, by electrical affinity, to form a rigid gel which is stable at high temperatures.
Meanwhile, solubility (or water-resistance) and tensile strength of the rayon fiber are changed by the content of chitosan and/or chitosan derivatives, or alginic acid and/or alginic acid derivatives of the aqueous cellulose solution. In order to provide water-resistivity, antibacterial property and tensile strength which are suitable for practical use, preferably, the content of chitosan and/or chitosan derivatives, or alginic acid and/or alginic acid derivatives is 0.1xcx9c50 wt % based on the total weight of the alkali cellulose and/or cellulose derivatives. If the content of chitosan and/or chitosan derivatives, or alginic acid and/or alginic acid derivatives is less than 0.1 wt %, antibacterial property is lowered. If the content thereof is more than 50 wt %, mechanical properties are lowered.